1. Field of the Invention
The inventions disclosed and taught herein relate generally to drill bits for drilling wells; and more specifically relate to monitoring the wear of drill bits for drilling wells in earth formations.
2. Description of the Related Art
U.S. Pat. No. 4,655,300 teaches “a method and apparatus for detecting excessive wear of a rotatable bit used in drilling. In particular, the apparatus can detect loss of gauge or bearing failure in a bit. The method is accomplished by connecting a restricting means in the drill bit that can be manipulated to reduce the flow of drilling fluid through at least one port in the drill bit. A wire is connected between a sensor which senses wear and the restriction means to cause the restriction means to reduce the flow of drilling fluid and thereby signal the surface by the reduced flow as an indication of wear.”
U.S. Pat. No. 4,694,686 teaches a “method and apparatus by which the degree of wear and useful life limitations of a drill, end mill or other types of metal removal tools can be detected. The method is based on the short circuit current, open circuit voltage and/or power that is generated during metal removal by the utilization of an insulated rotary tool bit to which electrical contact is made by a non-rotating conductor and an insulated or non-insulated workpiece, with an external circuit connecting the tool and workpiece through a measuring device. The generated current, voltage or power shows a sharp increase or change in slope upon considerable tool wear and/or at the point of failure.”
U.S. Pat. No. 4,785,894 teaches an “earth drilling bit incorporating a bit wear indicator. The bit wear indicator includes: a sensor to detect wear at a selected point on the bit; a device for altering the resistance of the bit to receiving drilling fluid from the drill string; and, a tensioned linkage extending between the wear sensor and the flow resistance altering means. On detecting a predetermined degree of wear, the wear sensor releases the tension in the tensioned linkage. This activates the flow resistance altering device, causing the flow rate and/or pumping pressure of the drilling fluid to change. This serves as a signal that the predetermined wear condition has been achieved. The bit wear indicator can be adapted to monitor many different types of bit wear, including bearing wear in roller-cone type bits and gauge wear in all types of bits.”
U.S. Pat. No. 4,785,895 teaches an “earth drilling bit incorporating a tensioned linkage type bit wear indicator. A tensioned linkage extends through the bit between a wear sensor and a device for altering the resistance of the bit to receiving drilling fluid from the drill string. On detecting a predetermined degree of wear, the wear sensor releases the tension in the tensioned linkage. This activates the flow resistance altering device, causing the flow rate and/or pumping pressure of the drilling fluid to change. The tensioned linkage passes through two intersecting passageways in the bit. A guide element is inserted at the intersection of the two intersecting passageways. The guide element routes the tensioned linkage between the two passageways.”
U.S. Pat. No. 4,786,220 teaches a “method and apparatus by which the degree of wear and useful life limitations of a drill, end mill or other types of metal removal tools can be detected. The method is based on the short circuit current, open circuit voltage and/or power that is generated during metal removal by the utilization of an insulated rotary tool bit to which electrical contact is made by a non-rotating conductor and an insulated or non-insulated workpiece, with an external circuit connecting the tool and workpiece through a measuring device. The generated current, voltage or power shows a sharp increase or change in slope upon considerable tool wear and/or at the point of failure.”
U.S. Pat. No. 4,928,521 teaches a “method is provided for determining the state of wear of a multicone drill bit. Vibrations generated by the working drill bit are detected and converted into a time oscillatory signal from which a frequency spectrum is derived. The periodicity of the frequency spectrum is extracted. The rate of rotation of at least one cone is determined from the periodicity and the state of wear of the drill bit is derived from the rate of cone rotation. The oscillatory signal represents the variation in amplitude of the vertical or torsional force applied to the drill bit. To extract periodicity, a set of harmonics in the frequency spectrum is given prominence by computing the cepstrum of the frequency spectrum or by obtaining an harmonic-enhanced spectrum. The fundamental frequency in the set of harmonics is determined and the rate of cone rotation is derived from the fundamental frequency.”
U.S. Pat. No. 5,216,917 teaches “a new model describing the drilling process of a drag bit and concerns a method of determining the drilling conditions associated with the drilling of a borehole through subterranean formations, each one corresponding to a particular lithology, the borehole being drilled with a rotary drag bit, the method comprising the steps of: measuring the weight W applied on the bit, the bit torque T, the angular rotation speed Ω of the bit and the rate of penetration N of the bit to obtain sets of data (Wi, Ti, Ni, Ωi) corresponding to different depths; calculating the specific energy Ei and the drilling strength Si from the data (Wi, Ti, Ni, Ωi); identifying at least one linear cluster of values (Ei, Si), said cluster corresponding to a particular lithology; and determining the drilling conditions from said linear cluster. The slope of the linear cluster is determined, from which the internal friction angle φ of the formation is estimated. The intrinsic specific energy E of the formation and the drilling efficiency are also determined. Change of lithology, wear of the bit and bit balling can be detected.”
U.S. Pat. No. 6,631,772 teaches a “system and method for detecting the wear of a roller bit bearing between a roller drill bit body and a roller bit rotatably attached to the roller drill bit body. A valve-plug is placed between the roller drill bit body and roller bit such that the valve-plug is removably fitted in a drilling fluid outlet in the roller drill bit body, and the valve-plug extends into a channel in the roller bit whereby uneven rotation or vibration of the roller bit causes the valve-plug to impact the sides of the channel which removes the valve-plug from the drilling fluid outlet to cause drilling fluid to flow through the drilling fluid outlet. The drop in pressure from the drilling fluid flowing through the drilling fluid outlet indicates that the roller bit is worn and may fail.”
U.S. Pat. No. 6,634,441 teaches a “system and method for detecting the wear of a roller bit bearing on a roller drill bit body where the roller element has a plurality of cutting elements and is rotatably attached to the roller drill bit body at the bearing. In the invention, a rotation impeder is in between the roller element and roller drill bit body and upon uneven rotation of the roller element which indicates that the roller element bearing may fail, the rotation impeder impedes the rotation of the roller element. The drill rig operator at the surface can cease drilling operations upon detection of the cessation of rotation of the roller element. The rotation impeder can also be seated in a drilling fluid outlet and cause a detectable loss in drilling fluid pressure when dislodged to otherwise cease rotation of the roller drill bit.”
The inventions disclosed and taught herein are directed to an improved method of monitoring the wear of drill bits for drilling wells in earth formations.